1. Field of the Invention
The invention relates to a method in charging a battery powered device and an apparatus for working said method.
2. Description of the Prior Art
If the battery in prior art battery powered devices having a built-in charge control circuit controlled by the device, and a switch for connecting the device including the battery to a battery charger, has been discharged to such extent that the voltage thereof is too low to feed the device and to activate the charge control circuit thereof in order to initiate normal charging of the battery over said circuit when the device is connected to the charger, it may be impossible to start the device even if it is connected to the charger, and thus to charge the battery.
When the battery powered device having an almost flat battery is switched on the behaviour of the device accordingly is upredictable. Will the device be switched on correctly? Will the extra current flow to the device caused by decoupling capacitors when the device is switched on lower the battery voltage even more?
Different alternatives are available in order to charge the battery in case the device is not able to initiate charging due to lack of enough power from the battery when the device including the battery is connected to the charger:
The battery is disconnected from the device and placed in a charger and then, when it has been charged, is replaced into the device. This must be done by the user himself, which makes the handling of the device more tedious; PA1 The device including the battery is connected to a charger which supplies a small trickle charge current which independently of the charge control circuit always charges the battery when connected to the charger. Eventually, the battery voltage will reach a level which is high enough in order to operate the device and initiate normal charging of the battery over the charge control circuit. In this case if the trickle charge current is supplied by a simple trickle charge resistor the trickle charge current has to be very low to prevent damage of the battery should the battery be charged already when it is connected to the charger. It follows that charging of a flat battery to switch-on level will take long time; PA1 The device is operated by the charging voltage which is applied directly to the device when the battery is connected to the charger. In this case the power supplied to the device cannot be controlled satisfactorily as to the quality thereof. PA1 The charging voltage is transformed to a high quality voltage used for operating the device when the battery is connected to the charger. This solution necessitates extra components to be included into the charger.